1. Field of the Invention
The present invention relates to an ultrasonic surgery apparatus for use in cataract surgery in which an opaque crystalline lens caused by a cataract is subjected to ultrasonic vibrations and emulsified, and then is aspirated and discharged outside a body.
2. Description of Related Art
In cataract surgery, an ultrasonic surgery apparatus is generally widespread which gives ultrasonic vibrations to nucleus of a crystalline lens using a tubular ultrasonic chip (referred to as an US chip, hereinafter) attached to a handpiece for surgery for performing fragmentation and emulsification, and aspirates and removes emulsified tissue of the nucleus of the crystalline lens through an aspiration hole at the tip of the US chip for discharging outside a body. In this kind of apparatus, a surgeon controls operations of irrigation liquid supply to an eye, aspiration, and phacoemulsification (induction of ultrasonic vibrations) using a footswitch having a pedal (see Japanese Patent Application Unexamined Publication No. Hei11-206803).
Besides, an ultrasonic oscillation mode in this kind of apparatus generally includes a pulse oscillation mode in which ultrasonic oscillation and intermission alternate (see WO95/20374 (Japanese Patent Application Unexamined Publication No. Hei9-508298)) in addition to a continuous oscillation mode in which ultrasonic oscillation is successively performed. In the pulse oscillation mode, nucleus followability of the US chip is improved and an amount of ultrasonic wave used is decreased, so that heat production may be suppressed to lower tissue invasion as compared with the continuous oscillation mode. Further, for the apparatus of WO95/20374, ultrasonic power and a pulse-duty ratio at the time of pulse oscillation (the ratio of oscillation to intermission) are changed in accordance with a vacuum (aspiration pressure) level which corresponds to a clogging condition of the US chip.
Incidentally, the ultrasonic power and the pulse-duty ratio are preferably low in view of the tissue invasion because fragmentation power relatively sufficient for soft nucleus of the crystalline lens may thereby be obtained. However, when great fragmentation power is required in such a case where hard nucleus of the crystalline lens is encountered, the conventional apparatus can increase (raise) the ultrasonic power only to a maximum value previously set through an operation panel even if the pedal is depressed. In this occasion, the surgeon instructs an operator of the apparatus (an assistant) to reset and raise the ultrasonic power and the pulse-duty ratio through the operation panel. However, this is troublesome and smooth surgery is difficult to perform.
Additionally, the apparatus of WO95/20374 has a constitution where the ultrasonic power and the pulse-duty ratio are automatically changed according only to the aspiration pressure level. Therefore, the ultrasonic power and the pulse-duty ratio happen to change contrary to the surgeon's intention.